Automatic interlock to facilitate automatic control of rolling mill with varying numbers of operational stands



3,387,4 72 'IONATIC CONTROL 0F ROLLING MILL WITH VARYING NUMBERS oF OPERATIONAL STANDS June l1. 1968 c. c. PULLEN AUTOMATIC INTERLOCK TO FACILITATE AU Sheets-Sheet l Filed Feb.

INVENTOR Char/es C Pcf//en June 1l. 1968 c. c. PULLEN 3,387,472

AUTOMATIC INTERLOCK TO FACILITATE AUTOMATIC CONTROL OF ROLLING MILL WITH VARYING NUMBERS 0F OPERATIONAL STANDS Filed Feb. 4, 1966 5 Sheets-Sheet l m. m u

.nl W DI ww /r m/ A N June 11. 1968 c. c. PULLEN 3,387,472

AUTOMATIC INTERLOCK TO FACILITATE AUTOMATIC CONTROL OF ROLLING MILLk WITH VARYING NUMBERS OF' OPERATIONAL STANDS 5 Sheets-Sheet 5 Filed Feb. 4, 1966 am T m IM A /0 NNW t WL W P Qww mwwwww w www www I C /m, @MWL www w s w e WHL W m. mww www www. N0 nvm, www www@ mmwt mww.\ qw l S www h www Sw bww l .im Y ||m W Ilm v @,N Q MWNVL NWN .www www w m Gw ww..w\ @w w \mw w n 2 Al www www @wh mwwvlw @wv/ w www Q www3 d: )mw l www w .W Y www vwww .4. p bwww ww u. \\w www Rw f u wwwa if www f A o V www www www WNW SIN o 0 o o United States Patent O AUTOMATIC INrEizLcK To FACILITATE AUTOMATIC CONTROL OF ROLLING MILL WITH VARYING NUMBERS OF OPERA- TIDNAL STANDS Charles Chester Pullen, Bethlehem, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware Filed Feb. 4, 1966, Ser. No. 525,082 4 Claims. (Cl. 72--1/1) This invention relates to automatic control of rolling mills and particularly to logic systems with alternate control sequences for controlling rolling mills.

In application Ser. No. 419,310, iiled Dec. 18, 1964 by the present inventor, now U.S. Patent No. 3,318,125, there is disclosed a control system for rolling mills, described with reference to a looper control system for rolling mills, wherein there is provided a logic sequence control means which controls the raising and lowering of the looper, and the initiation and termination of control of the speed of a mill stand by movements of the looper, according to signals received from strip detectors mounted on mill stands on either side of the looper. The logic system prevents the reraising of the looper once it is lowered or reinitiation of speed control by the looper once it is discontinued unless a certain sequence of signals has been received. This sequence control prevents the raising of the looper or reinitiation of speed control in the interval between two closely following strips.

Because of the speed of the strip through the mill it is preferable for the strip detection signal arising from the stand preceding lthe looper to come from the second mill stand preceding the looper, rather than the stand immediately preceding the looper, in order to provide better mill operation. This arrangement was disclosed in the above referred to application. At times, however, it is convenient for various reasons in normal rolling mill practice to dummy, or completely deactivate, one or more mill stands in a rolling mill. If a duinmied stand happens to also be the stand on which is mounted a strip detector for a looper control or other control system, the detector will also usually be deactivated, particularly if it cornprises the popular load cell type detector. A strip detection signal must -then necessarily be taken from another mill stand to replace the unavailable signal. This has caused difficulty since readjustment of the logic system is invariably necessary and a manual switching means must 'be provided to switch to the alternate detector. An operator is apt to forget to throw a manual switch with the result that the logic system is thrown out of coordination or completely blocked. The present inventor has now devised a logic arrangement which allows the system to be operated from an alternate strip detector with-out .adversely atecting the coordination of the system and without the necessity for the operator remembering to throw a manual switch.

It is an object of the present invention therefore to provide a novel interlocking logic circuit for automatic control of rolling mill systems, such as looper control systems, in which operation of the mill system will not be reinitiated once operation has been discontinued until a strip detector associated with a stand preceding the mill system indicates that a strip is entered in that stand and a strip detector associated with a mill stand following the mill system has detected a strip in the mill after a period in which no strip has been detected in the following mill stand and in which the operative signal indicating the presence or absence ofthe strip in a mill stand prior to the mill system maybe received from one or more of several alternate detectors.

3,387,472 Patented June 11, 1968 "ice The control system of the present invention comprises control apparatus to operate a rolling mill system, and a logic element sequence control system t-o appropriately activate and deactivate the control apparatus in response to signals received from strip detectors associated with individual mill stands.

Referring to the drawings:

FIGURE l diagrammatically shows a portion of a rolling =mill train having a looper control system with which is -associated the automatic sequence control of the present invention.

FIGURE 2 is a diagram of speed control circuits for the looper control system of FIGURE l.

FIGURE 3 diagrammatically shows the logic control circuit which controls the contacts in the speed control circuit of FIGURE 2 and operates valves to raise and lower vthe loopers.

In FIGURE 1 are shown four rollingI mill stands numbered 5 to 8 which may constitute a portion of a finishing train of a hot rolling mill. Each mill stand is supplied with a screw control mechanism, shown diagrammatically, and a screw setting, valso shown diagrammatically, -by Iwhich the distance between the rolls is .adjusted to control the gauge of the strip leaving the mill.

Each of the mill stands has a load cell associated with it, the signals of which indicate to the sequence control system :the presence or absence of strip in each respective mill.

Between each mill stand is diagrammatically shown a looper. No. 1 looper is located between mill stands `5 and `6, looper No. 2 'between mill stands 6 and 7, and looper No. 3 between mill stands 7 and 8. Each looper may be raised `and lowered by a conventional pneumatic cylinder arrangement, not shown, as is well known in the looper art. The valves controlling the admission of air to the pneumatic cylinder arrangement are controlled by solenoids operated 'by the static element logic circuit hereinafter described. As shown in FIGURE 1 the speed matching controller controls a speed regulator which in turn determines, together with the speed. setting, the speed of the mill motor, not shown, which drives the rolls in the mill stands. The speed of each mill stand is controlled through the speed matching controller within a range determined by the speed setting, l`by movements of the looper following the mill stand.

The tail end of a strip A is shown just passing through mill stand 8 `while the forward `portion of the following strip B is shown passing through stands 5, 6 and 7.

The operation of the sequence control of the present invention for the control of a mill system will be described with respect to the automatic contr-ol of looper No. 2 which controls the speed of mill stand 6 in FIGURE 1.

In FIGURE 2 is shown a speed control circuit for an individual looper by which the speed of a mill motor may Ihe controlled. The particular circuit shown in FIGURE 2 is the control circuit by which looper No. 2 in FIGURE 1 controls the mill motor of stand 6 to regulate slack between stands 6 and 7. The control circuit of FIGURE 2 is diagrammed in a simplified manner in. order to facilitate understanding. A somewhat more sophisticated speed control is shown in the above referred to application, and it will be understood that any similar speed control circuit may be equally satisfactory.

In FIGURE 2 is shown a looper contact arm 13 which is mechanically coordinated with movements of looper No. 2 in FIGURE l to move across resistance 17 of bridge circuit 15. A second contact arm 19 is manually movable across a second resistance 21 of bridge circuit 1S to provide a set point. Resistances 17 and 21 are connected in parallel across low voltage direct current source 23 through relay contact 31 of relay 325 later described.

Contact arms 13 and 19 are connected together through load resistor 25 to taps 27 and 29 appearing at the bridge output. Tap 27 is connected to contact 33 of synchronous converter 35 through line 37, capacitor 43, contact 41, shunting resistor 44, and resistor 45. Tap 29 is connected to common 47 which is grounded at 49.

Vibrating contact 51 of synchronous converter 35 alternately taps the potential at contacts 33 and 53 of synchronous converter 35 and applies the selected potentials through coupling capacitor 55 to grid 57 of tube 59, the plate of which is connected to a potential source B+. It Will be understood that tube 59 is the first tube of A.C. amplifier 61 shown symbolically in series with the lead 70 from cathode 69 of tube 59 to transformer 65 via lead 73. Transformer 65 couples A.C. amplifier 61 to a demodulator 67 which may be of any suitable form to convert the amplified alternating current signal to a direct current control signal. Cathode 69 of tube 59 is connected through a biasing network to grid 57 and also to common 47 through line 71.

Line 75 connects one output side of demodulator 67 to a control coil 77 of magnetic amplitier 79 which couples an A.C. power source 81 to speed regulator 83 through coils 85 and 87 respectively. Speed regulator 83 may comprise a magnetic amplifier, rectifier, and field exciter, not shown, which apply direct current to motor iield 89 to regulate the speed of armature 91 of mill motor 93, shown in dotted outline. Manual speed adjustment 95 may be used to vary the speed of mill motor 93.

Line 97 connects the other output side of demodulator 67 directly to common 47 through switch 99, normally closed during automatic operation, and resistor 101. A second path for current from line 97 to common 47 is provided through tap 103, resistor 105, contact 107, normally open during automatic operation, and resistors 109 and 111. Tap 113 provides an alternate path for the return of current to demodulator 67 through variable resistor 115, constituting a dummy load, and line 75 when contact 107 is closed during manual operation. Current also passes from demodulator 67 to common 47 during automatic operation via tap 117, resistor 119, and potentiometer 121.

Potential is tapped oiir potentiometer 121 and applied through capacitor 123, contact 125, normally closed during automatic operation, and resistor 127, to contact 53 of synchronous converter 35. A line 129 also leads to line 37 through contact 131, normally open during automatic operation, but closed during manual operation. Contact 53 of synchronous converter 35 is also connected to common 47 through resistor 133, variable resistor 135, and contact 137, normally closed during automatic operation. There is a third connection to contact 53 of synchronous converter 35 through line 139, and contact 141, normally open during automatic operation, to tap 143 located between resistors 109 and 111. Contact 33 of synchronous converter 35 is connected to common 47 during manual operation through resistor 45, contact 145, normally open during automatic operation, and line 147.

During manual operation a D.C. power source 149 is connected to common 47 through potentiometer 151, line 153, contact 155, normally open during automatic operation tap 117, and resistor 101.

Contacts 131, 41, 145, 125, 137, 141, 99, 155 and 107 are shown ganged together and operated by relay 341 shown in FIGURE 3. Contact 31 is shown operated by relay 325, also shown in FIGURE 3. As will be made clear hereinafter, contacts 41, 131, 137, 125 and 141 for best operation of the system should open and close with a slight delay over the other contacts operated by the same solenoid. Any suitable means may be used to provide the delay.

In FIGURE 3 two alternating power supplies 201 4 and 203 are shown connected by a double switch R205 to a standard volt 60 cycle source. A low voltage line connects terminal 207 of .power supply 201 and .terminal 209 of power supply 203. Line 211 passes to a control pulpit shown in dotted outline at 213 where the voltage in the line is applied in parallel across a switch R215, which manually activates automatic looper control operation, and a switch R217, which activates a manual controlled operation of the looper. Swith R215 operates a relay 219, which in turn operates switch 1.221. Switch R217 activates relay 223, which in turn operates switch L225. The circuit is completed by line 227 which returns to terminal 229 of power supply 203.

Switch L221 in the static logic circuit activates automatic control of the looper system. When switch L221 is closed, a signal is applied from common 231 to NOR logic elements 235 and 237. Since it is the characteristic of NOR elements not to give out an energization signal unless a zero signal is applied to all their inputs, NOR element 235 provides a zero signal to the B inputs of NOR elements 239 and 241, while NOR element 237 provides a zero signal to the B inputs of NOR elements 243, 245 and 247. NOR elements 239, 241, 245 and 247 are thereby placed in a 1st go condition so that a second zero signal applied at their other input will result in an energization signal being given out, and NOR element 24-3 is placed in a 2nd go condition so that zero signals to its other inputs will cause it to give an energization signal.

Switch L225 activates manual control through the logic element circuit rather than automatic control. If switch L225 is closed, an impulse is applied to NOR element 237. NOR 237 will provide a zero signal to the B input of NOR 243 in the same manner as in automatic placing it in a lst go condition. The energization impulse from switch L225 is also applied through line 249 to NOR 251, OR 253 which acts merely as a signal collector or combiner, and NOR 255, and through line 257 to OR 259 and NOR 261.

Terminal 263 receives a signal from load cell 5A in FIGURE 1 whenever there is strip in mill stand No. 5. This energization signal is applied to NOR 265, which, as a result, provides a zero signal to input A of NOR 241, and through timer 2'67 to NOR 269 which consequently provides an energization signal to input A of NOR 271.

1f the logic system is in automatic as a result of switch L221 being closed so that NOR 241 is in go condition, the application of a zero signal to its input A will result in NOR 241 providing an energization signal to input A of NOR 261, which as a result will provide a zero signal to input A of NOR 273 of memory element 275. Ordinarily when this first occurs, no signal is being received from terminal 274, which receives a signal from load cell 7A shown in FIGURE 1 if there is strip in mill stand No. 7. Since no energization signal is being received from terminal 274, and if manual control switch L225 is not closed, NOR 251 will be receiving a zero signal at both inputs and will be providing an energization signal to input A of NOR 239, which will consequently be providing a zero signal to, and through, OR 259 and timer 276 to NOR 277, which, in turn, will be providing an energization signal to input A of NOR 279 of memory element 275, through line 281 to input A of NOR 283 and one input of OR 253, and through line 285 to input A of NOR 287 of memory element 289. Since NOR 279 of memory element 275 is receiving an energization signal at its A input, it necessarily puts out a zero signal which is applied to input B of NOR 273, which is also receiving a zero signal at its A input as a result of a strip signal being received from terminal 263. NOR 273 therefore puts out an energization signal which is applied to NOR 291 and input B of NOR 279. NOR 291 applies a zero signal through line 293 to input A of NOR 295, through timer 297 to NOR 299, and through timer 297 and line 301 to input A of NOR 303. NOR 299 as a result of the zero signal puts out an energizatio-n signal through line 395 to input A of NOR 307. NOR 273 of memory element 275 also applies an energization signal via line 309 to input A of NOR 311.

NOR 265, meanwhile, as a result of the strip indicating or energization signal received from terminal 263, also directs a zero signal to the input of NOR 269 through timer 267. NOR 269 consequently applies an energization signal to input A of NOR 271, which, as a consequence, applies a zero signal to the input of NOR 313. NOR 313 places an energization signal on input A of NOR 315 of memory element 289. NOR 315, consequently, puts out a zero signal to input B of NOR 237 of memory 289, to the input of NOR 317, and via lines 319 and 321 respectively to the B inputs of NORs 303 and 295. NOR 317 directs an energization signal via lines 323 and 324, respectively, to the B inputs of NORs 307 and 311.

Since NOR 303 is receiving zero signals at inputs A and B, it directs an energization signal to NOR 255 which, consequently, applies a zero signal to the input of NOR 322 and through line 326 to input C of NOR 243 to place NOR 243 in second go condition. NOR 322 directs an energization `signal to input `E of NOR 283, which is also receiving an energization signal at input A from NOR 277, directs a zero signal to input A of NOR 245, which is also receiving a zero signal at input B, and, as a result of having two zero inputs, directs an energization or current signal to AC. amplifier 328 to operate relay 325 which closes contact 31 to energize bridge circuit shown in FIGURE 2.

Meanwhile, since both inputs of NOR 295 are receive ing zero signals, NOR 295 directs an energization signal to NOR 327, which, as a consequence, directs a zero signal to the input of NOR 329, which, in turn, sends an energization signal to input A of NOR 331 of memory element 333. NOR 331, therefore, directs a zero signal to input B of NOR 335 of memory element 333. If the system is set for automatic control, a zero signal will be received at input B of NOR 247. With no signal being received from terminal 274, indicating no load on load cell 7A, NOR 277 directs an energization signal through line 231 or OR 253 which directs this energization signal to input A of NOR 247. NOR 247 consequently directs a zero signal to the input of NOR 337, which, in turn, applies an energization signal to input A of NOR 335 of memory element 333. NOR 335, therefore, directs a zero signal to input B of NOR 331 of memory element 333, and also to amplifier 339, which, as a consequence, prevents relay 341 from operating.

Since, when strip is entered only in stand No. 5, no signal will be received at terminal 274 from load cell 7A, NOR 251 will provide an energization signal to input A of NOR 243, providing manual contact 1.225 is open. When NOR 243 receives an energization signal at input A it necessarily has a zero output even though it is in a second or double go condition as a result of zero signals being received at its B and C outputs. The zero output is applied to amplifier 343 which as a consequence does not operate solenoid 345.

Solenoid 345 operates a pneumatic air valve, not shown, to direct air from a suitable source to a pneumatic cylinder to raise looper No. 2. The pneumatic arrangement for raising the looper is well known and is therefore not illustrated. Any suitable arrangement known to the art may be used. If it is desired to accelerate the raising of tl e looper a looper boost arrangement may be added to the logic element system such as is shown in connection with the logic system shown in the present inventors above referred to copending application.

Since when strip is entered only in stand No. 5, no signal will be received at terminal 347 from load cell 6A, NOR 349 will provide an energization signal to NOR 247 via OR 253, and to input B of NOR 271. These signals have no effect since NOR 247 is already receiv ing an energization signal from NOR 277 via line 281 and OR 253 as a result of the zero signal at terminal 274, and NOR 271 is already receiving an energization signal at input A as a result of the signal received at terminal 263 and passed on by NOR 265, timer 267 and.NOR 269.

The elements of the logic control system have been described above with respect to a rst condition Where strip has entered mill stand No. 5 when this stand is not dummied so that an energization signal is received by NOR 265 from terminal 263. If, however, stand No. 5 is dummied, no sif'nal will be received at any terminal until the strip reaches stand No. 6. Since a zero signal is being received from terminal 263 it will readily be seen that the signal output of NOR 273 of memory element 275 will be reversed to zero and, consequently, the signal at the A inputs of each of NORS 311, 295, 3137, and 363 will be reversed from that described with respect to their condition when a signal is received from load cell 5A through terminal 263. When strip enters stand No. 6 a signal is received at terminal 347 and the input of NOR 349 and, as a result, NOR 349 provides a zero signal to NOR 247 through OR 253, and to input B of NOR 271. Since no signal is being received at terminal 263, input A of NOR 271 is receiving a zero signal. NOR 271, consequently, upon receiving two zero signals, puts ut an energization signal, and, as will be readily understood, the output of NOR 315 of memory element 239 is switched to an energization signal. As a result, the signals to the B inputs of NORs 311, 295, 307 and 303 are switched from that condition described with respect to a signal being received from load cell 5A via terminal 263. Since NOR 307 now receives a zero signal at both inputs, it puts out an energization signal to NOR 255 which directs a zero signal to input C of NOR 243 placing this NOR in a second go condition. NOR 322 at the same time directs an energization signal to input B of NOR 233, which, as a consequence, directs a zero signal to the A input of NOR 245.

Both inputs of NOR 311 also receive zero signals causing NOR 311 to direct an energization signal to NOR 327 which therefore directs a zero signal to the input of NOR 329, which consequently puts out an energization signal to the A input of NOR 331. This is the same signal as is received when terminal 263 is energized. Memory circuit 333 is thus in the same condition and directs a zero signal to amplifier 339.

It will be seen from the above that relay 341 is not energized, relay 325 is energized and NOR 243 is in second go condition just as when terminal 263 is energized from load cell 5A, and the control functions of the logic circuit are consequently exactly the same as if a signal had been received from terminal 263 instead of terminal 347.

It will be seen that when under either of the above described conditions a signal is received at terminal 274 from load cell 7A indicating that strip is entered in mill stand 7, NOR 251 will direct a zero signal to input A of NOR 239 which, since it is also receiving a zero signal at input B, as a consequence of the system being placed in automatic control condition by switch L221, directs an energization signal through OR 259 and timer 276 to NOR 277, which directs a zero signal to input A of NOR 279 of memory element 275, to input A of NOR 283, to input A of NOR 247 via OR 253, and to input A of NOR 287 of memory element 239.

lf No. 5 mill stand is not dummicd, the zero signal to input A of NOR 287 has no effect on memory system 289, because, although the output of NOR 287 is thereby switched to an energizatlon signal directed to input B of NOR 315, the output of NOR 315 was already Zero due to the energization signal received at input A derived from the energization at terminal 263 and load cell 5A. When strip drops out of stand 5, on the other hand, and the signal to input A of NOR 315 switches to zero, input B has previously been placed on a holding euergization signal so that the output from NOR 315 still remains zero. In fact, it will be noted, that as long as stand No. is not dimmied the output from NOR 315 will always be zero no matter what combination of signals is received from the three terminals 274, 263, and 347. It will be evident, therefore, that the signals to the B inputs of NORs 311, 295, 307, and 303 remain the same under all around sequences of mill operation.

The zero signal to input A of NOR 279 when strip enters stand #7 does not affect memory element 275, bccause the B input of NOR 279 continues to receive a holding energization signal from NOR 273, which signal is also applied to NOR 291. As a consequence the A inputs of NORs 311, 295, 307, and 333 remain the same as when strip is entered in stand 5 only.

The A input of NOR 331 of memory element 333 receives an energization signal when strip is first entered in stand 5, while input A of NOR 335 receives an energization signal derived from NOR 277 through NOR 247. When strip enters stand 7, input A of NOR 335 receives a zero input, and, since input B has been receiving a zero holding impulse from NOR 331, its output is switched to an energization impulse and applied as a holding energization impulse to input B of NOR 331, and as an energization impulse to amplifier 339, which amplifies the current and operates relay 341 to open and close the proper contacts in the looper speed control, shown in FIGURE 2, to place the speed control in automatic operation.

The zero signal from NOR 251 derived from the energization signal from terminal 274 is also applied to input A of NOR 243, which, since it is already in a double go condition, puts out an energization signal, which is amplitied by amplifier 343, and operates solenoid 345 to raise No. 2 looper into contact with the strip.

It will be noted that while a zero impulse is directed to input A of NOR 243 immediately, and looper No. 2 consequently begins to raise to contact the strip as soon as a signal is received from terminal 274, timer 276 delays the passage of the energization signal from NOR 239 to NOR 277 for a predetermined period, so that the zero signal from NOR 277, which eventually reaches input A of NOR 335, is delayed for a sufiicient period so that the looper has a chance to contact the strip before the speed control is switched on automatic.

As in the above referred to copending application, when strip drops out of stand No. 5 the signal to imput A of NOR 273 switches from zero to an energization signal. The output from NOR 273 consequently goes from zero to an energization signal, and is applied as a holding signal to NOR 279 and an energization signal to NOR 291. The A inputs of each of NORs 311, 295, 307, and 303 are consequently switched so that none has a double Zero input and they all apply a Zero signal to either NOR 327 or NOR 255. NOR 255 receiving all zero inputs applies an energization signal via line 326 to input C of NOR 243, which consequently puts out a zero signal to amplifier 343 so that solenoid 345 is deenergized and looper No. 2 lowers as the air pressure is removed from its pneumatic cylinders. The change of signal from NOR 255 is delayed for a predetermined period by timer 297, so that the looper does not begin to descend when the strip drops out of stand 5, but begins to descend only soon enough to be down when the strip drops out of stand 6. The point where it begins to descend is shown as point C on FIGURE l. The Output of NOR 329 will be switched t0 a zero signal immediately, as it is not delayed by timer 297, but will have no immediate effect on memory element 333, because input B of NOR 331 continues to receive an energization hold signal from NOR 335, both inputs of which have zero signals, even though input A of NOR 331 receives a zero signal. NOR 335 continues to put out an energization signal to amplifier 339, holding relay 341 closed, until the strip drops out olf stand 6. When the strip drops out of stand 6 the energization signal is removed from terminal 347, placing an energization signal on input A of NOR 247, which results in an energization signal also being placed on the A input of NOR 335. This causes NOR 335 of memory circuit 333 to immediately put out a Zero signal, and relay 341 is deenergized to switch the speed controller of FIGURE 2 to manual preset speed control. When NOR 255 switches its output from zero to an energization signal, after the delay occasioned by timer 297 to allow the strip to travel to point C in FIGURE 2, NOR 322 switches to a zero signal which is applied to input B of NOR 233, which, as a consequence of receiving a zero signal at input B from NOR 277, switches to an energization output signal which is converted to a zero signal at NOR 245 and applied to relay 325 which is deenergrzed and opens contact 31 in FIG- URE 2. This causes the speed control to hold to the last controlled speed of the mill motor until the strip drops out of Stand 6, when as described, the control is switched to manual preset control.

It will be noted that in the above referred to copending application, when the signal to the A inputs of the lower NORs of the memory elements corresponding to memory elements 275 and 333 is switched as a result of strip dropping out of the first and second stands, a hold condition is sct up in the memory elements by the switching of their outputs, and their outputs can only be changed again by the strip dropping out of stand No. 7, or the last controlling stand in the case of the first memory element, and the switching of the first memory element in the case of the third memory element. The operation of the present logic system is substantially similar, but the drop out signal can be received from either the #5 or #6 stand,

If mill stand No. 5 is dummied, no energization signal will be received from terminal 263. In this case input A of NOR 273 of memory element 275 will continue to receive an energization signal under all conditions, and NOR 273 will provide a zero signal to NOR 291 under all conditions. It will be seen, therefore, that with No. 5 mill stand dummied, the A inputs of NORs 311, 295, 307, and 303 will always receive the same signals. When strip enters stand No. 6 and a signal is received from terminal 347, a zero signal will be applied to input B of NOR 271, which is already receiving a zero signal at input A as a result of the Zero signal at terminal 263. NOR 271 consequently applies an energization signal to the input of NOR 313, which directs a zero signal to input A of NOR 315 of memory element 289. NOR 287 of memory element 289 is receiving an energization signal at input A from NOR 277, as a result of no strip being yet entered in mill stand No. 7, and NOR 287 is consequently directing a zero hold signal to input B of NOR 315. NOR 315, now receiving zero signals at both inputs, directs an energization hold signal to input B of NOR 287 and an energization signal to NOR 317. It will be seen that as a consequence the signal to each B input of NORs 311, 295, 307 and 303 is switched, and that NORs 311 and 307 each acquire zero signals at both of their inputs. These NORs thus direct energization signals to NORs 327 and 255 respectively with the result that an energization signal is directed to input A of NOR 331 -of memory element 333 and to input B of NOR 283, and a zero signal is directed to input C of NOR 243 in the same manner as occurs if memory element 275 is activated by terminal 263. Also in the same manner, when a signal is received at the A inputs of NORs 287 and 335 from terminal 274, indicating that strip has entered mill stand No. 7, nothing occurs with respect to NOR 287, while NOR 335 is switched to operate relay 341, but when strip drops out of stand No. 6, and the signal at terminal 347 is lost, the outputs of both memory elements change to lower the looper, in this case immediately, as timer 297 which delays the lowering controlled by memory circuit 275 is not in the circuit, and to operate relay 341 in order to place the speed control circuit in FIGURE 2 on manual preset speed control.

Relay 325, in the case of operation of the system from signals derived from terminals 274 and 347 alone, operates at the same time as relay 341, that is when the strip drops out of stand 6, rather than some time after it drops out of stand 5, but before it drops out of stand 6. This is because there is no need for a hold speed control period while the looper is lowering but the strip is still in stand 6. All operations take place simultaneously as the strip drops out of stand 6.

It will be noted that if strip is detected again by load cell 6A before the strip drops out of stand 7, the looper cannot be reraised or automatic speed control reasserted because of the energization hold signal at input B of NOR 315 derived from NOR 287.

It will often be found desirable to add a reset circuit such as shown in FIGURE 3 of the above referred to copending application for the purpose of directing a reset impulse to timer 276, NOR 279 of memory element 275, and NOR 331 of memory element 333, in order to reset these units with a standard pulse at the beginning of operation if the power has been interrupted for some reason. It may also be desirable to include a master switch to apply power to the magnetic amplifiers through the operation of an additional relay operated through the logic system, as shown in the copending application, only when the system is on automatic, and to operate the speed Icontrol only when desired even though the looper raise system is operative.

Referring now to FIGURES l through 3 with reference to operation of the complete system, it will be seen that when strip enters stand 5, if this stand is not dummied, a signal will be received at terminal 263 which will be applied through NORs 265 and 241, if the system is set to automatic, to memory element 275 which will set to one of its bistable conditions and provide a signal through NORs 307 and 255 to place NOR 243 in a second go condition. At the same time relay 325 is activated to close contact 31 and apply power to bridge circuit from D.C. source 23 in FIGURE 2. An energization signal is also received at input A of NOR 271, and this NOR, through NOR 313, activates memory element 289 in such manner that the B inputs of NORs 311, 295, 307 and 303 are placed in a signal condition which they maintain thereafter as long as stand 5 is not dummied. Memory element 333 is activated, but relay 341 is not closed until a signal is received from terminal 274 indicating that strip has entered stand 7 in FIGURE l. At this time solenoid 345 is operated through NOR 243 to raise the looper into contact with the strip and relay 341 is operated from memory element 333 to close contacts 41, 125, 137 and 99 in the speed control circuit in FIGURE 2.

When contact 41 is close-d a potential is applied to contact 33 of synchronous converter 35. The movement of contact 51 of synchronous converter 35 alternately compares the magnitude and polarity of this potential with that occurring on contact 53, and alternately applies the potentials through capacitor 55 to grid 57 of amplifier tube 59. An AC. current signal is thereby developed and amplified and then-after further amplification in amplifier 61-applied to demodulator 67 through transformer coupling 65, Demodulator 67, which may be of any suitable type, puts out a direct current proportional in magnitude to, and of the polarity of, the algebraic difference of potential between contacts 33 and 53 of synchronous converter 35. This is applied to coil 77 of magnetic amplifier 79 where it controls the current applied to mill motor 93 from power source 81. The control current returns to demodulator 67 through common 47, resistor 101, and closed contact 99. A small portion of the current also returns through closed Contact 99 via potentiometer 121, resistor 119, and tap 117. A potential is tapped off potentiometer 121 and applied via capacitor 123, closed contact 125, and resistor 127, to contact 53 of synchronous converter 35. This provides the feedback voltage for the system. Since potentiometer 121, in effect, measures the potential difference between common 47 and tap 117, it will be seen that, as demodulator 67 directs more current to magnetic amplitier coil 77 to control the speed of motor 93, a greater and greater potential will be applied to contact 53 until the potential is equal in magnitude to that on contact 33. The greater potential is applied immediately to contact 53 through capacitor 123. At the same time, however, the potential difference between common 47 and contact 53 is slowly equalized through resistor 133, variable resistor and closed contact 137. This offsets the potential received from potentiometer 121 and, if the potential from bridge circuit 15 has not reached a null point through movement of looper arm 13, the cycle will be repeated until it does. The time necessary for the potential on both sides of capacitor 123 to equalize is set by variable resistor 135. This sets the cycle of repetition of the control system.

When the rear end of the strip drops out of mill stand 5, the potential at terminal 263, in FIGURE 3, drops to zero, the output from memory element 275 is switched, and the memory placed in one of its bistable conditions such that only a change -in signal derived from the terminal 274 can switch it back. As a result of the switch in output of memory 275, the output of NOR 329 is switched to activate memory 333, and the output of NOR 255 is switched, after a delay occasioned by timer 297 to allow the end of the strip to reach point C, to switch the output of NOR 243 and lower the looper by deactivating solenoid 345. The 4output of NOR 322 is switched after the same `delay occasioned by timer 297, and, by switching NORs 283 and 245, deenergzes relay 325. This opens Contact 31 in bridge circuit 15 in FIGURE 2 so that the potential at contact 33 of synchronous converter 35 no longer follows the movement of looper arm contact 13. At the same time the last instantaneous potential on line 37 is held by capacitor 43 for a. sufiicient period of time to maintain substantially this potential on contact 33, and therefore hold the last controlled speed of motor 93 of stand 6, until the strip drops out of stand 6.

When the strip drops out of stand 6 the signal at terminal 347 is switched and the output of memory 333 is consequently switched to energize relay 341. Energization of relay 341 opens switches 41, 125, 137 and 99 to efectively isolate bridge circuit 15 from contact 33, to disconnect contact 53 from potentiometer 121 and common 47, and to remove the output of demodulator 67 from magnetic amplifier coil 77. At the same time contacts 131, 145, 141, and 107 are closed. It is preferable for contacts 145, 99, 155 and 107 to operate slightly in advance in order to allow time for their circuits to clear before applying a new charge thereto. Any suitable delay arrangement may be provided for the other contacts.

Contact 155 applies current from direct current source 149 to coil 77 of magnetic amplifier 79 via potentiometer 151, tap 117, resistor 101 and common 47. Adjustment of potentiometer 151 will consequently control the speed of motor 93.

A portion of the current from D C. source 149 is returned from common 47 via resistors 111, tap 143, resistor 109, tap 113, and variable resistor 115. At the same time the output from demodulator 67 is applied across dummy load variable resistor 115 through closed contact 107 and resistor 105. A portion of the current from demodulator 67 through dummy load 1.15 is returned to demodulator 67 via resistor 109, tap 143, resistor 111, common 47, resistor 101, tap 117, closed contact 155, line 153, potentiometer 151 and line 75. Common 47 is connected to contact 33 of synchronous converter 35 through closed contact switch 145. Potential from tap 143 is applied through closed contact 141 and resistor 127 to contact 53 of synchronous converter 35. Since current from demodulator 67 and direct current source 149 pass through resistors 109 and 111 in opposite directions, a null point may be reached by varying the current in either circuit, at which null point the potential at tap 143 and in common 47 are of the same magnitude, and the potential on contacts 33 and 53 of synchronous converter 35 are of the same magnitude. The output of demodulator 67 will therefore follow the output of direct current source 149, seeking the null point, so that when the control system is switched back `to automatic control there Will be a so-called burnpless transfer. Some current from the two circuits also passes through potentiometer 121 and potential from here is applied across capacitor 123 to capacitor 43 so that capacitor 43 already has a charge when the system is switched back to automatic control. During automatic operation, contact 41 is open and contact 145 is closed thereby allowing the charge on capacitors 43 and 123 to maintain a prescribed potential across resistor 44 to common 47.

When the strip leaves stand 7 the signal from terminal 274 switches the hold condition of memories 275 and 333 so that a signal indicating that a strip is in stand 6 may begin the entire cycle again.

When stand 5 is dummied no signal is received from this stand, and, as previously described, memory 275 continues to put out the same signal under all conditions. This places the A inputs of NORs 311, 295, 307 and 303 in a constant signal condition. Entrance of strip into stand 6 then switches memory 289 so that NOR 243 is placed in second go condition and memory 333 is activated. Relay 325 will have been deactivated before so that contact 31 in bridge circuit 15 of FIGURE 2 is closed. When strip enters stand 7, NOR 251 applies a zero energization signal to input A of NOR 243, which activates solenoid 345 to raise the looper into contact with the strip. When strip enters stand 7 the output of NOR 277 is also switched, after a short delay occasioned by timer 275, and a signal is applied to NOR 247 switching the output of memory 333 to operate relay 341 to switch to automatic speed control as described with respect to operation when stand 5 is not dummied. When strip drops out of stand 6 the signal to memory 289 is switched immediately without the time delay occasioned by timers 267 and 297 which occurs when strip drops out of stand S. Relays 341 and 325, and solenoid 345 are, therefore, all switched at the same time to lower the looper, switch the control to manual preset speed control and to remove the power source fro-m bridge circuit 15. Memories 289 and 333 are at the same time placed in one of their bistable conditions such that their output cannot be switched without a change in the signal received from the load cell associated with stand 7. When such signal is received, however, a subsequent signal indicating that that strip is entered in both stands 6 and 7 will begin the entire cycle of looper raise and automatic speed control again.

If switch L225 in FIGURE 3 is closed by operating switch R217, an energization impulse will be applied to NOR 237, NOR 277 through timer 276 and OR 259, NOR 261, NOR 251, NOR 247 through line 249 and OR 253, and NOR 255. Switch L221 will now be opened by operating switch R215 when R217 is closed. This will produce an energization pulse to the B inputs at NORs 239 and 241. It will be readily seen that the combination of signals will raise the looper but will prevent the speed control from switching to automatic since line 249 supplies an energization signal to the A input of NOR 247 to prevent relay 341 from being energized.

I claim:

1. In a strip rolling mill comprising a rst roll stand, a second roll stand, a third roll stand, and a control system to control an operation of a mill system including the following means for controlling said operation of the mill, means associated with the first stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative cf the absence of strip in the stand,

means associated with the third stand for generating a 'lrst signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, and

rst logic circuit means for controlling said operation of the mill in response to the following signals from said signal generating means,

a signal from the iirst stand indicatinf7 the presence of strip therein, a signal from the third stand indicating the absence of strip therein, and a subsequent signal from said third stand indicating the presence of strip therein, the improvement comprising:

(A) means associated with the second stand for generating a first signal indicative of the presence of strip in the stand and a second signal indicative of the absence of strip in the stand, and

(B) second logic circuit means for controlling said operation of the mill system in response to the following signals from said signal generating means associated with the second and third stands when, but only when, no signal is received from the signal generating means associated with the first stand indicating the presence of strip therein prior to the reception of a signal from the second stand, viz.

(i) a signal from the second stand indicating the presence of strip therein,

(ii) a signal from the third stand indicating the absence of strip therein, and

(iii) a subsequent signal from the third mill stand dicating the presence of strip therein.

2. A strip mill and control system for controlling a mill system according to claim 1 wherein the mill system comprises a looper located between said second and third mill stands, the raising of which looper is controlled by said signal sequence.

3. A strip mill and control system for raising a looper according to claim 2 wherein said rst and second logic circuits comprise static logic circuits.

4. The strip mill and control system for raising a looper according to claim 3 additionally comprising:

(C) a third static logic circuit means effecting control of the speed of stand 2 by the movements of the looper in response to the following signals from said signal generating means, viz.

(i) a signal from the second mill stand indicating the presence of strip therein when, but only when, a similar signal has not already been received from the iirst mill stand,

(ii) a signal from the third mill stand indicating the absence of strip therein,

(iii) a subsequent signal from said third stand inindicating the presence of strip therein, and

(iv) a continuing signal from the second mill stand indicating the presence of strip therein.

References Cited UNITED STATES PATENTS 3,036,480 5/1962 Schwab 72-11 3,188,841 6/1965 Wallace 72-17 3,318,125 5/1967 Pullen u- 72-14 RICHARD I. HERBST, Primary Examiner.

A. RUDERMAN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,387 ,472 June ll 1968 Cllarles Chester Pullen It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 47, "of the following" should read of a following Column 5 line 24 "input B of NOR 283)" should read u input B or NOR 283. NOR 283, which line 43, "line 281 or OR 253" should read line 281 to OR 253 Signed and sealed this 25th day of November 1969.

(SEAL) Attest:

Edwin. member, Jr. l i WILLIAM E. SCHUYLER, JR.

Attcsting Officer Commissioner of Patents awww. 

1. IN A STRIP ROLLING MILL COMPRISING FIRST ROLL STAND, A SECOND ROLL STAND, A THIRD ROLL STAND AND A CONTROL SYSTEM TO CONTROL AN OPERATION OF A MILL SYSTEM INCLUDING THE FOLLOWING MEANS FOR CONTROLLING SAID OPERATION OF THE MILL, MEANS ASSOCIATED WITH THE FIRST STAND FOR GENERATING A FIRST SIGNAL INDICATIVE OF THE PRESENCE OF STRIP IN THE STAND AND A SECOND SIGNAL INDICATIVE OF THE ABSENCE OF STRIP IN THE STAND, MEANS ASSOCIATED WITH THE THIRD STAND FOR GENERATING A FIRST SIGNAL INDICATIVE OF THE PRESENCE OF STRIP IN THE STAND AND A SECOND SIGNAL INDICATIVE OF THE ABSENCE OF STRIP IN THE STAND, AND FIRST LOGIC CIRCUIT MEANS FOR CONTROLLING SAID OPERATION OF THE MILL IN RESPONSE TO THE FOLLOWING SIGNALS FROM SAID SIGNAL GENERATING MEANS, A SIGNAL FROM THE FIRST STAND INDICATING THE PRESENCE OF STRIP THEREIN, A SIGNAL FROM THE THIRD STAND INDICATING THE ABSENCE OF STRIP THEREIN, AND A SUBSEQUENT SIGNAL FROM SAID THIRD STAND INDICATING THE PRESENCE OF STRIP THEREIN, 